With a nozzle head of the aforedescribed type, the air which is directed toward the path of the curtain of filaments which descend from the horizontal elongated spinneret effects a cooling of the melt of the thermoplastic synthetic resin as it emerges from each of the orifices to cause the melt to congeal and to draw the congealing filaments. The filaments are collected below the head on a conveyor or the like to form a non-woven mat, web or fleece of the filaments.
A meltblowing process utilizing an apparatus of this type is described in EP 0377 926 A1.
The nozzle head of this apparatus comprises a bar-shaped horizontal spinneret with its orifices in a row along a wedge-shaped, downwardly converging formation, the spinneret or orifice bar or beam being supplied with the thermoplastified synthetic resin as a hot melt.
The spinneret is flanked by two blowing devices, each of which can comprise a housing supplying the blowing air, and means forming blowing slits to either side of the orifice row, training the air toward the curtain of filaments and directing the air along this curtain.
The means forming the nozzle slits can each include a blowing lip defining the blowing slit with the aforementioned formation, the lower ends of the blowing lips having a spacing from the apex and this formation which is referred to as the setback. The setback or offset for a particular application can be the width of the blowing slit.
When the arrangement of EP 0 377 926 A1 is used, the setback generally ranges from a tenth of a mm to several tenths of a mm.
The system of EP 0 377 926 can provide say 100 screws for controlling the thickness of the respective blowing slit and has a number of drawbacks, not the least of which is an inability to conveniently maintain or clean the slits and the region between the lips from particles of the synthetic resin material and other contaminants which may or may not adhere to the various surfaces but tend to accumulate in the very narrow clearances defined between the lips and the wedge-shaped formation. The contaminants tend to produce irregularities in the blowing air flow and the reliability of the apparatus, while also interfering with the uniformity of the product.